A Rohm Trainer .177 airgun. The model is based on a .22LR pistol of almost identical design, but this one takes .177 pellets and a bottel of CO2. I've edited out the rotary magazine to give it a little more authenticity.
I got it from a friend of mine quite a few years ago. I would imagine that being a resident of the USA, you can probably get the .22LR version, rather than have to settle for the puny .177 CO2 powered version that we get in the UK.
Try contacting GalleryOfGuns.com and see if they can source something similar for you.
Blackpool Air Rifles [link] stock the Rohm Twinmaster Trainer, and as long as you're over 18 you can buy one. I think it has to be sent to a local firearms dealer though, stupid UK laws mean that they can't just send it straight to you any more.